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Distinct tissue-specific requirements for the zebrafish tbx5 genes during heart, retina and pectoral fin development.

Pi-Roig A, Martin-Blanco E, Minguillon C - Open Biol (2014)

Bottom Line: However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed.Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed.Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

View Article: PubMed Central - PubMed

Affiliation: CSIC-Institut de Biologia Molecular de Barcelona, Department of Developmental Biology, Parc Científic de Barcelona, C/Baldiri Reixac, 10, Barcelona 08028, Spain.

ABSTRACT
The transcription factor Tbx5 is expressed in the developing heart, eyes and anterior appendages. Mutations in human TBX5 cause Holt-Oram syndrome, a condition characterized by heart and upper limb malformations. Tbx5-knockout mouse embryos have severely impaired forelimb and heart morphogenesis from the earliest stages of their development. However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed. We identified a novel tbx5 gene in zebrafish--tbx5b--that is co-expressed with its paralogue, tbx5a, in the developing eye and heart and hypothesized that functional redundancy could be occurring in these organs in embryos with impaired tbx5a function. We have now investigated the consequences of tbx5a and/or tbx5b downregulation in zebrafish to reveal that tbx5 genes have essential roles in the establishment of cardiac laterality, dorsoventral retina axis organization and pectoral fin development. Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed. Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

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tbx5 morphants exhibit cardiac jogging and lefty2 expression defects. (a–a″) tbx5a morphant phenotypes. (b–b″) tbx5b morphants. (c–e″) Left, right and middle jog phenotypes obtained by co-injection of tbx5a and tbx5b MOs at 0.5 ng (c–c″), 1.5 ng (d–d″) or 3 ng (e–e″) of each MO. (f) Control (ctrl) morphant. (g) Quantification of the phenotypes. (h–j) lefty2 expression in control (h) and double-morphant (i,j) 22-somite stage embryos. (k) Quantification of the phenotypes. A χ2 test has been used to assess significant differences between groups (**p < 0.001). All images are dorsal views with anterior to the top, and myl7 expression is used to highlight the developing heart tube in a–f.
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RSOB140014F2: tbx5 morphants exhibit cardiac jogging and lefty2 expression defects. (a–a″) tbx5a morphant phenotypes. (b–b″) tbx5b morphants. (c–e″) Left, right and middle jog phenotypes obtained by co-injection of tbx5a and tbx5b MOs at 0.5 ng (c–c″), 1.5 ng (d–d″) or 3 ng (e–e″) of each MO. (f) Control (ctrl) morphant. (g) Quantification of the phenotypes. (h–j) lefty2 expression in control (h) and double-morphant (i,j) 22-somite stage embryos. (k) Quantification of the phenotypes. A χ2 test has been used to assess significant differences between groups (**p < 0.001). All images are dorsal views with anterior to the top, and myl7 expression is used to highlight the developing heart tube in a–f.

Mentions: As heart looping orientation phenotypes are indicative of cardiac left–right asymmetry defects, we decided to examine whether heart jogging, the first morphologically evident break in the left–right symmetry of the zebrafish heart tube, was disrupted after knock-down of tbx5 genes. To this end, heart laterality was assessed at 26 hpf using myl7 expression to reveal positioning of the heart tube and cardiac jogging was classified as left (normal), right (reversed) or midline (no jog). After injection of 3 ng of control MO, 99% (n = 197) of the embryos developed normal left jogging (figure 2f,g). By contrast, right as well as midline jogging phenotypes were observed after tbx5a knock-down (figure 2a–a″,g; n = 183). Similarly, tbx5b morphants displayed left as well as right and middle jogging of their linear heart tubes (figure 2b–b″,g; n = 90).Figure 2.


Distinct tissue-specific requirements for the zebrafish tbx5 genes during heart, retina and pectoral fin development.

Pi-Roig A, Martin-Blanco E, Minguillon C - Open Biol (2014)

tbx5 morphants exhibit cardiac jogging and lefty2 expression defects. (a–a″) tbx5a morphant phenotypes. (b–b″) tbx5b morphants. (c–e″) Left, right and middle jog phenotypes obtained by co-injection of tbx5a and tbx5b MOs at 0.5 ng (c–c″), 1.5 ng (d–d″) or 3 ng (e–e″) of each MO. (f) Control (ctrl) morphant. (g) Quantification of the phenotypes. (h–j) lefty2 expression in control (h) and double-morphant (i,j) 22-somite stage embryos. (k) Quantification of the phenotypes. A χ2 test has been used to assess significant differences between groups (**p < 0.001). All images are dorsal views with anterior to the top, and myl7 expression is used to highlight the developing heart tube in a–f.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043114&req=5

RSOB140014F2: tbx5 morphants exhibit cardiac jogging and lefty2 expression defects. (a–a″) tbx5a morphant phenotypes. (b–b″) tbx5b morphants. (c–e″) Left, right and middle jog phenotypes obtained by co-injection of tbx5a and tbx5b MOs at 0.5 ng (c–c″), 1.5 ng (d–d″) or 3 ng (e–e″) of each MO. (f) Control (ctrl) morphant. (g) Quantification of the phenotypes. (h–j) lefty2 expression in control (h) and double-morphant (i,j) 22-somite stage embryos. (k) Quantification of the phenotypes. A χ2 test has been used to assess significant differences between groups (**p < 0.001). All images are dorsal views with anterior to the top, and myl7 expression is used to highlight the developing heart tube in a–f.
Mentions: As heart looping orientation phenotypes are indicative of cardiac left–right asymmetry defects, we decided to examine whether heart jogging, the first morphologically evident break in the left–right symmetry of the zebrafish heart tube, was disrupted after knock-down of tbx5 genes. To this end, heart laterality was assessed at 26 hpf using myl7 expression to reveal positioning of the heart tube and cardiac jogging was classified as left (normal), right (reversed) or midline (no jog). After injection of 3 ng of control MO, 99% (n = 197) of the embryos developed normal left jogging (figure 2f,g). By contrast, right as well as midline jogging phenotypes were observed after tbx5a knock-down (figure 2a–a″,g; n = 183). Similarly, tbx5b morphants displayed left as well as right and middle jogging of their linear heart tubes (figure 2b–b″,g; n = 90).Figure 2.

Bottom Line: However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed.Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed.Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

View Article: PubMed Central - PubMed

Affiliation: CSIC-Institut de Biologia Molecular de Barcelona, Department of Developmental Biology, Parc Científic de Barcelona, C/Baldiri Reixac, 10, Barcelona 08028, Spain.

ABSTRACT
The transcription factor Tbx5 is expressed in the developing heart, eyes and anterior appendages. Mutations in human TBX5 cause Holt-Oram syndrome, a condition characterized by heart and upper limb malformations. Tbx5-knockout mouse embryos have severely impaired forelimb and heart morphogenesis from the earliest stages of their development. However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed. We identified a novel tbx5 gene in zebrafish--tbx5b--that is co-expressed with its paralogue, tbx5a, in the developing eye and heart and hypothesized that functional redundancy could be occurring in these organs in embryos with impaired tbx5a function. We have now investigated the consequences of tbx5a and/or tbx5b downregulation in zebrafish to reveal that tbx5 genes have essential roles in the establishment of cardiac laterality, dorsoventral retina axis organization and pectoral fin development. Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed. Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

Show MeSH
Related in: MedlinePlus